Stents and other medical devices are used for re-establishment of a proper blood flow in a blocked artery in interventional cardiological procedures, such as, percutaneous transluminal coronary angioplasty. However, the existing interventional cardiological procedures and cardiological medical devices used in these procedures are associated with phenomenon like restenosis. In order to reduce the instances of restenosis that occur following angioplasty procedures or stent deployment Drug Eluting Stents (DESs) are often used. The current DESs are loaded with drugs with the help of polymers. The polymers may trigger inflammation at a site where the DESs are implanted. In certain instances, the inflammation triggered by the DESs may be more severe than the inflammation that is caused by bare metal stents owing to the presence of polymers in the DESs. The inflammation triggered by the polymers may in turn lead to thrombus formation because of body's physiological immune response. The thrombus thus formed may be an acute thrombus or a sub-acute thrombus. The thrombus may further aggravate resulting into blockage of the artery. In addition, the DESs with non-degradable polymers are associated with late inflammation reactions, thereby resulting in late thrombus formation. Thus, the polymers used for loading the drugs on the DESs may lead to restenosis.
In order to avoid the inflammation that is associated with the use of the polymers for loading the drug on the stent, the drug may be loaded on surface of the stent without using polymers. However, the methods for loading the drug on the surface of the stent without using the polymers that are known in the art are based on modifying the surface of the stent.
In addition, the presence of one or more drugs and the polymers on an inner surface of the stent results in a delayed healing or an improper healing of the lesions as compared to the bare metal stents. A long-term anti-platelet (e.g. Clopidrogel) therapy is generally advised in patients with the delayed healing or the improper healing. The anti-platelet therapy is also associated with side effects and thus is not advisable for long-term.
Further, the particle sizes of the drugs as well as the polymers that are coated on the DESs are larger than the sizes of the tissue pores at a target site. Therefore, a substantial amount of the drugs remain unabsorbed. The unabsorbed drugs may get washed away in blood stream and may produce side effects. For example, currently used DESs are loaded with more than 100 micro-grams of a drug out of which, only 12 nanogram to 25 nanogram of the drug penetrates the tissues of the artery. Rest of the drug is either washed away in the blood stream from the inner surface of DESs or is released over time.
Further, the currently used DESs are associated with phenomenon like focal restenosis and edge restenosis. One of the major reasons for focal restenosis is that some portions of the lesion are adequately supplied with the drug by the DESs while some portions of the lesion (region not covered by the DES) are very poorly or not at all supplied with the drug by the DESs. The portions of the lesion that are adequately supplied with the drug may possibly remain less prone to restenosis as compared with the portions of the lesion that are poorly supplied or not at all supplied with the drug.
In the current DESs, the drug is coated on the metal surface. The amount of the drug that reaches the lesion is generally equal to a metal to artery ratio. The metal to artery ratio for the current DESs generally ranges from 10% to 20%. Thus, only 10% to 20% of the lesion is supplied with the drug. Whereas, the remaining 80% to 90% of the lesion is either very poorly supplied with the drug or not at all supplied with the drug. Further, owing to a larger particle size of the drug coated on the surface of the DESs, an optimum diffusion of the drug into the tissues of an artery is not achieved. The diffusion of the drug into the tissues of the artery further depends on properties of the drug. For example, sirolimus eluting stents exhibit a poor diffusion of sirolimus into the tissues of the artery because of low solubility associated with sirolimus. Therefore, sirolimus eluting stents may exhibit focal restenosis that is as high as 71% of the total restenosis. Whereas, paclitaxel eluting stents may exhibit focal restenosis that is as high as 56% of the total restenosis. Additionally, most of the drugs that are administered to a patient using the current DESs are hydrophobic in nature and have less affinity for body tissues. As a result, a high amount of the drug needs to be loaded in the DESs for achieving the desired therapeutic effect.
Therefore, there is a need in the art for an improved drug-delivering insertable medical device associated with reduced instances of focal restenosis, edge restenosis, total restenosis, acute thrombus formation, sub-acute thrombus formation, late thrombus formation, delayed healing of lesions, and improper healing of lesions. Further, an improved drug-delivering insertable medical device is needed in the art that may reduce the duration of anti-platelet therapy otherwise advised to patients with the delayed healing of lesions and/or the improper healing of lesions post deployment of the DES. In addition, an improved drug releasing medical device that provides for enhanced bioavailability of the drugs, enhanced biocompatibility and delivery of a drug to maximum portion of a lesion in the blood vessel with optimum drug loading is also needed in the art.